In conventional LED displays three well-chosen primary colors are used to produce a wide range of colors. The three well-chosen primary colors, when added together in the appropriate proportions, can approximate many of the colors that a human can perceive. This is a thoroughly studied area of human perception that is explained by the fact that the human eye perceives color using three different types of sensors called cones. A human perceives color when any or all of these three types of cones are stimulated. Theoretically, if three light sources, in this case LEDs, can individually stimulate these three different kinds of cones, all human perceivable colors could be duplicated. In practice, however, light sources because of certain deficiencies, cannot produce the stimuli needed to reproduce all colors.
An LED display is typically made up of various dots arranged in a matrix pattern having rows and columns. The dots are usually called pixels where the pixels are made up of several LEDs. The individual LEDs emit light of three basic colors: red, green and blue. Typically, each pixel is composed of at least one LED of each color. The intensity of the LEDs is usually controlled by controlling the current to the individual LEDs. This is sometimes referred to as controlling the drive to an LED. A pixel can produce a specific perceived color by varying the drive to the three colors of LEDs that comprise the pixel. Thus, by controlling the current drive to each of the LEDs that makes up a pixel and in turn controlling each of the pixels that make up a matrix of pixels, an LED display device is capable of displaying a plurality of colors and light intensities so as to realize, for example, a multi-color display. A large LED display can contain hundreds of thousands of pixels and millions of LEDs.
In an LED display, each of the pixels and each of the LEDs must be controlled. Accordingly, prior art systems utilize a display driver in conjunction with a decoder and microprocessor for controlling the device to each LED of a display. U.S. Pat. NO. 5,612,711 (the “711” patent), entitled “Display System,” describes an example of such a prior art system. The '711 patent discloses an apparatus and method for driving LEDs of different colors in a matrix of pixels. Differently colored LEDs are commonly connected so that a voltage applied to one LED is applied to all the commonly connected LEDs. Drivers provide different voltages to different color LEDs in the matrix of LEDs. A processor controls the overall operation of the LED display.
Prior art displays, however, suffer from several deficiencies. Prior art LED displays that use three color of LEDs have a limited color gamut, significantly less than that able to be perceived by humans. Furthermore, prior art systems suffer from poor quality control in the transferring of original artwork to a display medium such as an LED display.
Prior art systems also suffer from undesirable artifacts such as contouring due to inappropriate luminance control at low brightness. Undesirable artifacts due to increments in dynamic range are called “contouring” because the increments in intensity produce what looks like flat regions in brightness with jumps or increments that look like contour lines.